1. Field of the Invention
The present invention pertains to an exhaust port assembly for use in a single-limb pressure support system, and, in particular, to an exhaust port assembly with enhanced noise reduction and gas diffusion capabilities, while also minimizing size. The present invention also pertains to a pressure support system using such an exhaust port assembly.
2. Description of the Related Art
It is well known to treat a patient with a non-invasive positive pressure support therapy, in which a flow of breathing gas is delivered to the airway of a patient at a pressure greater than the ambient atmospheric pressure. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the airway of a patient throughout the patient's respiratory cycle to treat obstructive sleep apnea (OSA), as well as other cardio-pulmonary disorders, such at congestive heart failure (CHF) and cheynes-stokes respiration (CSR). An example of such a CPAP device is the REMstar® and Solo® family of CPAP devices manufactured by Respironics, Inc. of Pittsburgh, Pa.
It is also known to provide a non-invasive positive pressure therapy, in which the pressure of gas delivered to the patient varies with the patient's breathing cycle. For example, a “bi-level” pressure support system provides an inspiratory positive airway pressure (IPAP) that is greater than an expiratory positive airway pressure (EPAP), which is the pressure is delivered during the patient's expiratory phase. Such a bi-level mode of pressure support is provided by the BiPAP® family of devices manufactured and distributed by Respironics, Inc. and is taught, for example, in U.S. Pat. No. 5,148,802 to Sanders et al., U.S. Pat. No. 5,313,937 to Zdrojkowski et al., U.S. Pat. No. 5,433,193 to Sanders et al., U.S. Pat. No. 5,632,269 to Zdrojkowski et al., U.S. Pat. No. 5,803,065 to Zdrojkowski et al., and U.S. Pat. No. 6,029,664 to Zdrojkowski et al., the contents of each of which are incorporated by reference into the present invention.
It is further known to provide an auto-titration positive pressure therapy, in which the pressure of the flow of breathing gas provided to the patient changes based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea or upper airway resistance. An example of a device that adjusts the pressure delivered to the patient based on whether or not the patient is snoring is the Virtuoso® CPAP family of devices manufactured and distributed by Respironics, Inc. This auto-titration pressure support mode is taught, for example, in U.S. Pat. Nos. 5,203,343; 5,458,137 and 6,087,747 all to Axe et al., the contents of which are incorporated herein by reference.
A further example of an auto-titration pressure support device that actively tests the patient's airway to determine whether obstruction, complete or partial, could occur and adjusts the pressure output to avoid this result is the Tranquility® Auto CPAP device, also manufactured by Respironics, Inc. This auto-titration pressure support mode is taught in U.S. Pat. No. 5,645,053 to Remmers et al., the content of which is also incorporated herein by reference.
Other modes of providing positive pressure support to a patient are known. For example, a proportional assist ventilation (PAV®) mode of pressure support provides a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing effort to increase the comfort to the patient. U.S. Pat. Nos. 5,044,362 and 5,107,830 both to Younes, the contents of which are incorporated herein by reference, teach a pressure support device capable of operating in a PAV mode. Proportional positive airway pressure (PPAP) devices deliver breathing gas to the patient based on the flow generated by the patient. U.S. Pat. Nos. 5,535,738; 5,794,615; and 6,105,573 all to Estes et al., the contents of which are incorporated herein by reference, teach a pressure support device capable of operating in a PPAP mode.
For purposes of the present invention, the phase “pressure support system”, “pressure support device,” or “positive pressure support” includes any medical device or method that delivers a flow of breathing gas to the airway of a patient, including a ventilator, CPAP, bi-level, PAV, PPAP, or bi-level pressure support system.
FIGS. 1 and 2 schematically illustrate two exemplary embodiments of conventional pressure support systems 30 and 30′, respectively; either of is capable of providing any of the above positive pressure support therapies. The primary difference between these two embodiments is the technique used to control the pressure or flow of breathing gas provided to the patient.
Pressure support systems 30 and 30′ include a pressure generating system, generally indicated at 32 and 32′, that receives a supply of breathing gas from a breathing gas source, as indicated by arrow A, such as ambient atmosphere, and creates a flow of breathing gas at a pressure greater than ambient atmospheric pressure. The flow of breathing gas from pressure generator is indicated by arrow B. A pressure generator 34, such as a blower, impeller, drag compressor, fan, piston, or bellows, or other device that achieves this result, creates the flow of breathing gas at a pressure greater than the ambient atmospheric pressure. An exit conduit 36 communicates the flow of breathing gas from an outlet of pressure generator 34. Pressure generator 34 is a commonly a blower in which a fan or impeller is driven by a motor operating under the control of a controller 38, which is typically a microprocessor capable of executing stored algorithms.
In FIG. 1, the pressure or flow of breathing gas delivered to the patient is controlled, at least in part, by a pressure/flow controller 40 in conduit 36. Pressure/flow controller 40 is typically a valve that controls the pressure or flow of breathing gas by (1) exhausting a portion of the flow of breathing gas to atmosphere or to the inlet of pressure generator 34, (2) restricting the flow of breathing gas through conduit, or (3) a combination of these two functions. Controller 38 directs the operation of pressure/flow controller 40 to regulate the pressure or flow of breathing gas provided to the patient. Examples of suitable pressure controllers are taught in U.S. Pat. No. 5,694,923 to Hete et al. and U.S. Pat. No. 5,598,838 to Servidio et al.
In FIG. 2, the pressure or flow of breathing gas delivered to the patient is controlled, at least in part, by controlling the operating speed of pressure generator 34. This motor speed control technique can be used alone to control the flow or pressure of the breathing gas provided to the patient or it can be used in combination with a pressure controller 40, as discussed above. For present purposes, the combination of a pressure generator 34 and any of the above described techniques for controlling the flow or pressure of breathing gas provided to the patient, e.g., motor speed control, a pressure controller, or both, are referred to collectively as the “pressure generating system” or “pressure generating means,” with the ultimate goal of the pressure generating system being to provide a flow of breathing gas to the airway of the patient at the desired pressure or flow rate.
A conventional pressure support system may also include at least one sensor capable of measuring a characteristic associated with the flow of breathing gas, the pressure of the breathing gas, a condition of a patient using the pressure support system, a condition of the pressure support system, or any combination thereof. For example, FIGS. 1 and 2 schematically illustrate a flow sensor 42 and a pressure sensor 44 associated with exit conduit 36. The output from such sensors are provided to controller 38 and used to control the rate of flow and/or pressure of the breathing gas delivered to the patient. For example, in a bi-level pressure support system, the transition from IPAP to EPAP and from EPAP to IPAP is triggered based on the changes in the patient's breathing cycle, which is detected by such sensors. For an auto-titration pressure support system, the output of one or more such sensors is used to determine when to raise and lower the pressure provided to the patient, and can be used to determine the magnitude of the change in pressure.
It is known that the location and number of such sensors can be other than that shown in FIGS. 1 and 2 while still providing feedback for the control of the pressure support system. For example, it is known to measure the pressure at or near a patient interface device 46, rather than near the pressure generating system 32, 32′, as shown. In addition, it is known to monitor the operation of pressure generator 34 to determine the condition of the patient, such as whether the patient in breathing on the system. In which case, the functions of the pressure and/or flow sensors are effectively incorporated into the pressure generator monitoring function.
Although sensors 42 and 44 are described above as being a flow and pressure sensor, respectively, it is to be understood that other types of sensors can be used in pressure support systems 30 and 30′. For example, a microphone can be provided to detect sounds produced by the patient, which can be used, for example, in an auto-titration pressure support system to control the pressure of the breathing gas delivered to the patient. See, e.g., U.S. Pat. Nos. 5,203,343 and 5,458,137 both to Axe et al., the contents of which are again incorporated herein by reference.
Other sensors that can be used with the pressure support system include a temperature sensor that senses the temperature of gas anywhere in the breathing circuit, a current and/or voltage sensor for sensing the current/voltage of the signal provided to the motor in the pressure generator, and a tachometer that detects the rotational speed of the motor. These sensors are used, for example, to sense the condition of the patient, the flow or pressure of gas provided to the patient, or the operation of the pressure support system. Still other external sensors can include EMG electrodes provided on the patient, a respiratory belt or other motion sensor that measures movement of the chest and/or abdomen, and a motion sensor to detect patient movement, such as leg movement.
Conventional pressure support systems 30 or 30′ also typically includes an input/output device 48 for communicating information to the user and for communicating information or commands to controller 38. An example of input/output device 46 is an LCD or LED display and manually actuated buttons provided on a housing, which is indicated by dashed line 50, of pressure support systems 30 and 30′. Of course, other types of input/output devices, such as a keypad, voice activated input device, audio outputs, lights, switches, and knobs are known for use in communicating information between the user and the pressure support device. In addition, a computer or printer terminal coupled to controller 38 can also constitute input/output device 48.
In a conventional pressure support system, a flexible conduit 52 is coupled to exit conduit 36. The flexible conduit forms part of what is typically referred to as a “patient circuit” that carries the flow of breathing gas from the pressure generating system to patient interface device 46. Patient interface 46 connects the patient circuit with the airway of the patient so that the elevated pressure gas flow is delivered to the patient's airway. Examples of patient interface devices include a nasal mask, nasal and oral mask, full face mask, nasal cannula, oral mouthpiece, tracheal tube, endotracheal tube, or hood.
In a non-invasive pressure support system, i.e., a system that remains outside the patient, a single-limb patient circuit, as shown in FIGS. 1 and 2, is typically used to communicate the flow of breathing (arrow B) with the airway of the patient. Because patient circuit 52 is a single-limb circuit, an exhalation port 54, also referred to as an exhalation vent, exhaust port, or exhaust vent, is provided in patient circuit 52 and/or patient interface 46 to allow exhaust gas, such as the exhaled gas from the patient, to exhaust to atmosphere, as indicated by arrow C.
A variety of exhalation ports are known for venting gas from a single-limb patient circuit. For example, U.S. Pat. No. Re. 35,339 to Rappoport discloses a CPAP pressure support system wherein a few exhaust ports are provided directly on the patient interface device, i.e., in the wall of the mask. However, these exhalation ports are relatively noisy due, for example, to the relatively turbulent passage of gas through the holes. In addition, this exhaust port configuration results in a relatively direct stream of exhaust gas being directed from the mask or patient circuit. Both noise and direct streaming of the flow of exhaust gas are undesirable, because a typical CPAP system is intended to be used while the patient is asleep. Sleep for the patient or the patient's bed partner is disturbed if there is excessive exhaust gas noise or if a stream of gas is directed at the patient or at the user's bed partner.
The exhaust port assembly described in published PCT application no. WO 98/34665 to Kwok attempts to minimize the noise associated with the leakage of exhaust gas. This is allegedly accomplished by providing an elastomeric ring around the perimeter of the exhaust vent. This exhaust port configuration, however, does not solve the problem of preventing a generally direct or concentrated stream of gas from being directed from the mask onto the user or the user's sleep partner.
U.S. Pat. No. 5,937,851 to Serowski et al., U.S. Pat. No. 6,112,745 to Lang, and published PCT application no. WO 00/78381 to Gunaratnam et al. all disclose exhalation ports for a positive pressure support system. Each of the exhalation ports taught by these references attempts to minimize noise by reducing the turbulence associated with the flow of exhaust gas through the exhalation vent. This is accomplished by providing a channel from the interior of the patient circuit to the ambient atmosphere that is specifically configured to baffle noise and/or reduce the turbulence in the exhaust flow. In addition, the exhalation ports taught by these references attempt to solve the problem of preventing a stream of gas from being directed onto the patient or onto the patient's bed partner by controlling the direction of the flow of exhaust gas. For example, each of these references teaches directing the flow of exhaust gas back along the patient circuit rather than directly outward away from the patient.
An exhaust vent entitled, “E-Vent N” and manufactured by Dräger Medizintechnik GmbH attempts to minimize noise by providing a large number of very small exhaust paths from the patient circuit to ambient atmosphere. More specifically, the E-Vent N exhaust port assembly includes several slits defined along the length of the patient circuit. Surrounding these slits are a number of rings that encircle the patient circuit and that are stacked one on top of the other. More specifically, each ring includes a series of grooves on its flat side, so that when the rings are stacked in this manner, the grooves in each ring form a very larger number of minutely sized exhaust paths to atmosphere, with the exhaust gas passing between adjacent rings. This configuration disperses the exhaust gas over a relatively large area due the large number of rings that are stacked on top of one another, so that the noise of the exhaust gas passing through the vent assembly is relatively low.
However, this exhaust port configuration is very complicated in that the stacked ring configuration is difficult to manufacture and maintain. Also, the minute exhaust paths defined between each ring are prone to clogging and cleaning is difficult. Finally, this design requires that the exhaust paths formed by the grooved rings occupy a relatively large area of the patient circuit to provide a sufficient flow of exhaust gas therefrom. This makes the exhaust port assembly bulky and heavy, and it does not minimize the amount of deadspace in the patient circuit.